Process for recovery of lithium from brine

ABSTRACT

A process for recovery of lithium ions from a lithium-bearing brine includes contacting the lithium-bearing brine with a lithium ion sieve (where that LIS includes an oxide of titanium or niobium) in a first stirred reactor to form a lithium ion complex with the lithium ion sieve, and decomplexing the lithium ion from the lithium ion sieve in a second stirred reactor to form the lithium ion sieve and an acidic lithium salt eluate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation-In-Part of copending application Ser.No. 16/410,523, filed on May 13, 2019, which is a Continuation-In-Partof copending application Ser. No. 16/224,463, filed on Dec. 18, 2018,which claims the benefit of U.S. Provisional Application No. 62/610,575,filed Dec. 27, 2017, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to methods for recovering ionsfrom brine, and more particularly, to methods for recovering lithiumions from brine.

2. Description of the Background Art

As a result largely of the recent interest in the use of lithium ionbatteries for electric vehicles and stationary electric power storageassociated with renewable energy systems including from wind, solar, andtidal sources, the demand for lithium has increased substantially andmay soon outstrip supply. There is potentially a large supply of lithiumavailable in various sources, such as seawater, brines, geothermalfluids, and continental salt lakes. As used herein, “brine” and “brines”refer to these various lithium-containing solutions. To date, however,there have been few viable ways to recover the lithium from thesesources without extensive concentration by evaporation, as the lithiumconcentrations in these resources are typically very low. In addition,the much higher concentration of other metal ions, such as sodium,potassium, calcium, and magnesium, interferes with recovery of thelithium.

Ion exchange is a well-known technology for recovery of lowconcentrations of metal ions from aqueous solutions. However,conventional ion exchange resins, such as strong acid cation exchangeresins with sulfonic acid functional groups and chelating resins withiminodiacetate groups, have a higher preference for multivalent ions,such as calcium and magnesium, which may be present. Although theselectivity for lithium over other monovalent ions, such as sodium andpotassium, may be similar, the presence of these competitive monovalentions, which normally exist in great excess in brines, makes recovery oflithium unfeasible.

Inorganic ion exchange media, such as ionic sieves, based uponmanganese, titanium, or other oxides, have been identified aspotentially useful for recovery of lithium from brines where thereexists high concentrations of competitive ions, such as calcium,magnesium, sodium, and potassium. These materials can be termed lithiumion sieves (LIS). LIS exhibit a high preference for lithium because theLIS exchange sites are so narrow that Na⁺ (0.102 nm), K⁺ (0.138 nm), andCa²° (0.100 nm), which have ionic radii larger than Li⁺ (0.074 nm),cannot enter the exchange sites. Although the ionic radius of the Mg²⁺(0.072 nm) ion is similar to the ionic radius of Li⁺, a high amount ofenergy is required for the dehydration of magnesium ions to allow it toenter the exchange sites so that selectivity over Mg²⁺ is maintained.

However, LIS have a number of disadvantages. First, they are weaklyacidic in nature and, as a result, have reduced capacity at lower pHlevels. Second, they are not stable in acid solutions since some of thecomponents dissolve in acid. As they degrade, they lose capacity to takeup lithium so that they must be replaced on a frequent basis. ReplacingLIS represents a significant cost. Moreover, removal and replacement ofthe degraded LIS, when it is installed in a conventional column, isdifficult and time consuming. Finally, LIS are synthesized as finepowders and, therefore, due to high pressure drop, cannot be used infixed beds, as is done with conventional ion exchange resins. A numberof attempts have been made to improve the form by, for example,granulation, foaming, membranes, fibers, and magnetization. However,when these powders are agglomerated into larger geometries, the kineticsare severely impaired as a result of blockage of the pores and activeexchange sites by the binding agents, and, typically, lower surface areato volume/mass ratio with larger particle sizes.

For example, the reference, Chitrakar et al., “Lithium Recovery fromSalt Lake Brine by H₂TiO₃ ,” Dalton Transactions, 43(23), pages8933-8939, Jun. 21, 2014 (hereinafter referred to as “Chitrakar”),relates to the synthesis, characterization, and laboratory evaluation oflithium selective adsorbents based upon metatitanic acid. However,Chitrakar does not mention an industrial process and does not discussissues concerning solid/liquid separation or washing the brine andeluent from the adsorbent on an industrial scale. For example,adsorption tests in Chitrakar were conducted in beakers at an adsorbentsolids concentration of 20 g/L, and elution tests with HCl wereconducted at an adsorbent solids concentration of 10 g/L. Chitrakar doesnot disclose how to use the adsorbent on a continuous industrial scale.Specifically, the laboratory filtration used in the tests would not beapplicable on an industrial scale.

As such, there is still a need to improve the method for recoveringlithium from brine using lithium ion sieves that overcome thedisadvantages above.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a process for recovery oflithium ions from a lithium-bearing brine by contacting thelithium-bearing brine with a lithium ion sieve for less than about onehour in a first mixed or stirred reactor to form a lithium ion complexwith the lithium ion sieve and decomplexing the lithium ion from thelithium ion sieve in a second mixed or stirred reactor to form thelithium ion sieve and an acidic lithium salt eluate.

In one embodiment, a process for recovery of lithium ions from alithium-bearing brine comprises contacting the lithium-bearing brinewith a lithium ion sieve for less than about one hour in a first mixedor stirred reactor to form a lithium ion complex with the lithium ionsieve. Then, the process includes a step of decomplexing lithium ionsfrom the lithium ion sieve in a second mixed or stirred reactor to forman acidic lithium salt eluate solution separated from the lithium ionsieve. The lithium ion sieve may comprise an oxide of titanium orniobium (e.g., metatitanic acid or lithium niobate).

The decomplexing may be performed by elution using an acid. Aconcentration of the acid may be maintained at a constant value throughadditions of said acid. The concentration of the acid should be lessthan 0.1 M and preferably at a pH of greater than 1 and less than 3 andmost preferably at pH of about 2. An average contact time of the lithiumion complex with the lithium ion sieve and the acid may be less than 1hour. The acid may be hydrochloric acid or sulfuric acid.

A pH of the first reactor may be maintained at a constant value throughaddition of an alkali. The pH may be maintained at the constant value ofgreater than 4 and less than 9 or greater than 6 and less than 8. Thealkali may be sodium hydroxide (NaOH), ammonium hydroxide, potassiumhydroxide, sodium carbonate, magnesium hydroxide, calcium hydroxide, oranhydrous ammonia. For example, the alkali may be sodium hydroxide at aconcentration of less than 8% w/w.

More than 90% of the lithium ion sieves may have an average particlediameter of less than 40 μm and more than 90% of the lithium ion sievesmay have an average particle diameter of greater than 0.4 μm. More than90% by volume of particles of the lithium ion sieve may be less than 100μm in diameter and greater than 0.5 μm in diameter. More than 90% byvolume of particles of the lithium ion sieve may be greater than 0.5 μmin diameter. The process may further comprise the step of removinglithium ion sieves having an average particle diameter of less than 1 μmbefore contacting the lithium-bearing brine with the lithium ion sieve.

The process may further comprise the steps of separating the lithium ioncomplex with the lithium ion sieve from the brine with a solid/liquidseparation device; and contacting the lithium ion complex with thelithium ion sieve with water before decomplexing in the second reactor.The process may also further comprise the steps of separating thelithium ion sieve from the acidic lithium salt eluate solution with asolid/liquid separation device; contacting the lithium ion sieve withwater after decomplexing in the second reactor to obtain a regeneratedlithium ion sieve and a dilute acid water wash; and adding theregenerated lithium ion sieve to the first reactor. This process mayfurther comprise the step of dewatering the lithium ion complex with thelithium ion sieve to a moisture content of less than 90% by weightbefore decomplexing the lithium ion from the lithium ion sieve in thesecond reactor. This process may also further comprise the step ofdewatering the regenerated lithium ion sieve before being added to thefirst reactor. The step of contacting the lithium ion sieve with watermay comprise contacting the lithium ion sieve with sufficient water suchthat more than 50% of the lithium ion that has been decomplexed from thelithium ion sieve is washed from the lithium ion sieve prior to addingthe regenerated lithium ion sieve to the first reactor. The step ofcontacting the lithium ion sieve with water may also comprise contactingthe lithium ion sieve with water in more than one counter-current stagesuch that more than 50% of the lithium ion that has been decomplexedfrom the lithium ion sieve is washed from the lithium ion sieve prior toadding the regenerated lithium ion sieve to the first reactor. Theprocess may also further comprise the step of adding the dilute acidwater wash and additional concentrated acid to the second reactor.

The first reactor may comprise ultrafiltration or microfiltrationmembranes. Air or other gas may be used to agitate contents of the firstreactor. A flux rate through the ultrafiltration membrane or themicrofiltration membrane may be greater than 30 LMH at transmembranepressures of less than 30 kPa.

A concentration of the lithium ion sieve may be greater than 50 g/L orgreater than 100 g/L.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to one of ordinary skill in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings that aregiven by way of illustration only and are thus not limitative of thepresent invention. In the drawings, like reference numerals are used toindicate like features in the various views.

FIG. 1 is a diagrammatic view of an exemplary lithium extraction systemfor the present process.

FIG. 2 is a graph showing the amount of metal ion uptake as a functionof pH.

FIG. 3 is a graph showing the amount of lithium and titanium extractedas a function of hydrochloric acid concentration.

FIG. 4 is a graph showing an exemplary LIS particle size distribution ofa sample of metatitanic acid lithium ion sieve taken after a few hoursof air agitation in a slurry.

FIG. 5 is a diagrammatic view of an alternative lithium extractionsystem for the present process.

FIG. 6 is a graph of lithium concentration as a function of time for anexemplary extraction trial.

FIG. 7 is a graph showing the amount of lithium and titanium extractedas a function of pH.

FIG. 8 is a graph showing the effect of contact time on lithium capacityand calcium separation.

DETAILED DESCRIPTION OF THE INVENTION

As a result of the disadvantages discussed above, lithium ion sieveshave not been applied widely to recovery of lithium from brine on anindustrial scale to date. The present invention overcomes thesedisadvantages, making the use of lithium ion sieves for selectiverecovery of lithium from brine more commercially feasible.

The average particle diameter of conventional ion exchange resins istypically about 400-1250 micrometers. The RECOFLO® short bed ionexchange process utilizes what is normally considered the finestparticles used in large-scale industrial applications. These particlestypically have an average particle diameter of 100-200 micrometers.

By comparison, the lithium ion sieves utilized in the present inventionare preferably in powder form. The average particle size of the powderdoes not necessarily have to be limited. However, the average particlesize is preferably less than about 100 μm, more preferably 10 to 100 μm,even more preferably 20 to 100 μm, and yet even more preferably 20 to 95μm. Further, the average particle size may be 0.4 to 40 μm. Forinstance, more than 90% (by volume) of the lithium ion sieve particlesmay be less than 100 μm in diameter and greater than 0.5 μm in diameter.In the same or different embodiments, more than 90% (by volume) of thelithium ion sieve particles may be greater than 0.5 μm in diameter.Since these materials are synthesized as powders, the cost ofagglomeration is avoided. Moreover, the higher surface area afforded bysuch a powder significantly improves the kinetics of the ion exchangeprocess. In other words, the lithium ion sieves are not a compositebound together with a polymer or other binding agent.

Various lithium ion sieves are potentially useful for lithium recovery.Exemplary LIS include, but are not limited to, oxides of manganese andtitanium. Specifically, an exemplary LIS may include an oxide oftitanium, preferably metatitanic acid (MTA). However, the presentinvention is equally applicable to other types of lithium ion sievemedia such as manganese oxide and lithium niobate (i.e., niobic acid).The lithium ion sieve may also comprise doping agents in addition to anoxide of titanium, niobium, or manganese. However, the content of thelithium ion sieve would be predominately an oxide of titanium, niobium,or manganese.

In one embodiment of the present invention, the powdered lithium ionsieve media may be contacted with a lithium-containing brine in astirred tank reactor (STR or reactor). For example, the reactor may be atank containing the liquid to be treated along with the lithium ionsieve. The lithium ion sieve may be maintained in suspension by a mixeror by fluidization by upward liquid or gas bubble flow, which providesintimate contact between the lithium ion sieve and the brine. The pH ofthe brine in the reactor may be maintained at a constant level throughadditions of an alkali, such as sodium hydroxide (NaOH), ammoniumhydroxide, potassium hydroxide, sodium carbonate, magnesium hydroxide,and calcium hydroxide. For example, the pH of the brine in the reactormay be maintained at greater than 5 and less than 9.

Many of the brines that can be treated with the present inventioncontain appreciable concentrations of magnesium. Neutralization of thebrine with an alkali may present some problems for brines that containhigh concentrations of magnesium. Although magnesium hydroxide does notnormally precipitate below a pH of about 8, when the alkali is added,localized high pH conditions at the point where the alkali contacts thebrine results in precipitation of magnesium hydroxide. Despite the factthat the pH of the bulk brine is below the theoretical precipitation pH,the precipitate does not quickly dissolve. The presence of magnesiumhydroxide causes a number of problems. For example, it can adhere to thesurface of the LIS, inhibiting uptake of lithium. If a membrane isutilized for solid/liquid separation, it can reduce the permeate fluxand possibly foul the membrane.

When sodium hydroxide is utilized, the magnesium hydroxide precipitationproblem is particularly acute and more pronounced at higher NaOHconcentrations. When 50% w/w NaOH is utilized, large quantities ofMg(OH)₂ are produced that do not re-dissolve. If a more dilute NaOHsolution is utilized, the quantity of Mg(OH)₂ produced is less and theMg(OH)₂ re-dissolves more quickly. If 4% w/w NaOH is utilized, only verysmall quantities of Mg(OH)₂ are produced, which re-dissolve in just afew seconds. As such, if sodium hydroxide is used, the sodium hydroxideis preferably at a concentration of less than 8% w/w.

Use of dilute NaOH is disadvantageous in that it dilutes the barrenbrine. In locations where the barren brine must be re-injectedunder-ground, the resulting brine over-volume can be problematic, asmore brine cannot be pumped back into the ground than was withdrawn.

This problem can be avoided by utilization of ammonia forneutralization. The ammonia can be in the form of anhydrous ammonia gasor liquid ammonium hydroxide so that the amount of brine over-volume isnegligible. Only small quantities of Mg(OH)₂ precipitate out at theinjection point, even if anhydrous ammonia gas or 30% ammonium hydroxideare used, and this precipitate re-dissolves quickly, having no negativeimpacts on the process.

After the ion exchange reaction has been completed, the lithium-depleted(i.e., barren) brine may be separated from the lithium ion sieve andremoved from the reactor by various means. For example, thebrine/lithium ion sieve slurry (i.e., loaded lithium ion sieve) may becontacted with water in an additional stirred reactor to remove residualbrine before proceeding to the next step. Where the particle size of thelithium ion sieve is greater than about 10 microns, gravitysedimentation can be used. Where the particle size is less than 10microns, filtration devices such as a rotary drum vacuum or belt filterscan be used. Where the particles size is less than 1 micron, membranefiltration may be used. Combinations of these solid/liquid separationdevices can be advantageously used. One example of a possiblesolid/liquid separation device may be a centrifuge.

After removal of the barren brine, the lithium ion sieve contained inthe reactor may be contacted with an eluent. This eluent may be, amongother things, an acid, such as hydrochloric acid (HCl) or sulfuric acid(H₂SO₄). For example, the acid may be added in a concentration in theorder of less than 0.1 M, preferably at a pH of greater than 1 and lessthan 3 and most preferably at a pH of about 2. Without intending to bebound to any particular theory, it is believed that the acid elutes(decomplexes) the lithium from the LIS, thus producing a concentratedlithium salt product solution and regenerating the LIS. As used herein,a “complex” is a combination of individual atom groups, ions, ormolecules that combine to create one large ion or molecule. As usedherein, “decomplexing” is the act of separating individual atom groups,ions, or molecules from such a large ion or molecule. Because of theselectivity of the lithium ion sieve for lithium over other metals, theratio of lithium to other metals may be appreciably higher in theproduct solution than the feed brine.

After the lithium ion sieve has been regenerated, the lithium ion sievecan be reused to treat more brine and extract more lithium.

In an embodiment of the invention, the process may be conductedcontinuously. Two reactor stages may be needed in such a continuousprocess. Brine may be fed continuously to a loading stage whereinlithium ion sieve is contacted with the brine as a continuously mixedslurry. Lithium ions may then be removed from the brine via uptake bythe lithium ion sieve, resulting in the barren brine and alithium-loaded LIS. The barren brine may then be separated from thelithium-loaded lithium ion sieve and removed from the reactor. Thelithium-loaded lithium ion sieve, now separated from the brine, may bepassed on to an elution stage.

Regarding the contact time between the brine and the lithium ion sieve,it is known that metatitanic acid lithium ion sieves have very poorkinetic properties. The lithium ions take a relatively long time todiffuse through the narrow exchange sites. One would therefore expectthe amount of lithium taken up by the LIS to increase with increasedcontact time in the brine. In fact, FIG. 4(b) of Chitrakar shows theeffect of contact time of LIS with brine. This data clearly shows thatthe amount of lithium taken up by the LIS increases with time and iswhat would normally be expected with any ion exchange sorbent. However,the effect of contact time on lithium uptake over time was found to havethe opposite effect as shown in FIG. 8 . Specifically, the lithiumcapacity decreases over time. As FIG. 8 shows, the lithium capacitydecreased from 15.5 mg/g at 1 hour to 12.5 mg/g at 2 hours and furtherdecreased to 12 mg/g after 71 hours. The Ca separation factor alsodecreases with contact time. More calcium and less lithium are taken upon the LIS as contact time increases. Perhaps given enough time, thelarger calcium ions slowly diffuse to the narrow exchange sites anddisplace lithium. This phenomenon may not have been observed inChitrakar since the brine of Chitrakar had a much higher lithiumconcentration and lower calcium concentration ([Li]=1630 mg/L, [Ca]=230mg/L) than the brine typically used in the present invention. In FIG. 8, the brine used in the experiment had a lithium concentration of 219mg/L and a calcium concentration of 34,500 mg/L. Thus, in order tomaximize lithium capacity and calcium separation, at least for brinescontaining relatively high calcium and low lithium concentrations (e.g.,brine obtained from the Smackover formation in southern Arkansas), thecontact time between the LIS and the brine should be less than about 1hour.

Eluent may be fed continuously to the elution stage, and thelithium-loaded lithium ion sieve removed from the loading stage may becontacted with the eluent as a continuously mixed slurry. The lithiumion sieve and liquid are separated, and this separated liquid (i.e., theeluate) is the lithium salt product solution.

The lithium content of the lithium ion sieve leaving the elution stageis appreciably reduced and, the lithium ion sieve may be recycled backto the loading stage for reuse. In this manner, the lithium ion sievemay be reused multiple times, and the process may be operatedcontinuously.

In one embodiment, additional stages may be utilized as shown in FIG. 1. Specifically, a feed brine flows through a line 2 into a first stirredreactor 4, which contains lithium ion sieve, as part of a loading stage.The lithium ion sieve is maintained in suspension by a mixer 6. Thebrine/lithium ion sieve slurry is maintained at a constant pH throughthe addition of NaOH via line 8. The lithium ion sieve loaded with brineflows through line 10 into an additional stirred reactor 12 as part of awashing stage. The barren brine is separated from the loaded lithium ionsieve and flows through line 14. The lithium ion sieve loaded with brineis maintained in suspension by a mixer 16. In the washing stage, theloaded lithium ion sieve is contacted with water via line 18 to wash thebrine from the lithium ion sieve, which is believed to reducecross-contamination of the lithium salt product with contaminant ionspresent in the feed brine. The washed and loaded lithium ion sieve flowsthrough line 20 into a second stirred reactor 22 as part of an elutionstage. The wash water is separated from the washed and loaded lithiumion sieve and flows through line 24 to return to the first stirredreactor 4. The washed and loaded lithium ion sieve is maintained insuspension by a mixer 26. In the elution stage, the washed and loadedlithium ion sieve is contacted with HCl via line 28 to elute the lithiumions from the lithium ion sieve. The concentration of acid in the secondstirred reactor 22 is maintained at a constant value through theaddition of HCl via line 28. The regenerated lithium ion sieve flowsthrough line 30 into another stirred reactor 32 as part of an acid washstage. The lithium ions, as LiCl product, are separated from theregenerated lithium ion sieve and flow through line 34. The regeneratedlithium ion sieve is maintained in suspension by a mixer 36. In the acidwash stage, residual acid is washed from the lithium ion sieve throughthe addition of water via line 38 so that the feed brine is notacidified in the loading stage when the lithium ion sieve is recycledand recovered lithium is not recycled back to the loading stage. Thewashed and regenerated lithium ion sieve flows through line 40 back tothe first stirred reactor 4 to be used again in the loading stage. Thedilute acid washings are separated from the washed and regeneratedlithium ion sieve and flow through line 44 to be used along with theadditional concentrated acid in the elution stage.

In one embodiment, several loading stages may be utilized in series andoperated counter-currently. The brine may be initially processed in afirst loading stage. The treated brine from the first loading stage,still containing some residual lithium, may be passed to a secondloading stage wherein contact with lithium ion sieve further reduces thelithium content of the brine. The lithium ion sieve from the secondloading stage, containing some lithium but still having further lithiumcapacity available, may be passed to the first loading stage. The loadedlithium ion sieve from the first loading stage may then be passed to anelution stage. By this means, the lithium content of the barren brinecan be further reduced. To further reduce the lithium content of thebarren brine, additional loading stages may be utilized in this manner.

The loaded lithium ion sieve can similarly be processed in severalelution stages whereby the lithium ion sieve passes counter-currently tothe eluate flow. By this means, the lithium content of the lithium ionsieve can be further reduced, and the lithium concentration in theeluate (i.e., the lithium product) can be increased.

The exchange reaction for uptake of the lithium ions onto the lithiumion sieve from the brine is shown in equation (1)LIS.H+Li⁺→LIS.Li+H⁺  (1)where LIS.H represents the lithium ion sieve in the freshly regenerated,hydrogen form and LIS.Li represents the lithium ion sieve in the loadedlithium form.

As the reaction proceeds, hydrogen ions are released to the brine,decreasing the pH of the brine. The active component of the lithium ionsieve may be, for example, an oxide of titanium, such as metatitanicacid (MTA). MTA is a weak acid and, therefore, has a high affinity forhydrogen ions. As a result, at a low pH, where hydrogen ions areavailable, MTA may not easily exchange hydrogen ions for lithium. Thelithium ion sieve may also further comprise small amounts of dopingagents.

FIG. 2 shows the amount of metal ion uptake as a function of pH. It canbe seen that lithium uptake is reduced significantly below a pH of about6.5 and little lithium will be taken up below a pH of about 4. As thelithium loading proceeds, the pH of the brine drops. When the pH dropsto a pH of about 4, no further uptake of lithium can occur.

This phenomenon is similar to that which is observed with conventionalpolymeric weak acid cation exchange resins. The conventional approach todealing with this issue is to pre-neutralize the ion exchange resin withsodium hydroxide, which converts the exchanger to the sodium form sothat, during loading, the pH of the solution remains constant. However,this approach will not work with a lithium ion sieve since the sodiumion is too large to penetrate the lithium ion sieve.

In one embodiment, the pH may be adjusted prior to contacting the brinewith the LIS by dosing the brine with NaOH or another base, such assodium carbonate or ammonium hydroxide, prior to treatment. Such apre-treatment will raise the initial pH so that the final pH will not beso low as to prevent lithium uptake. The disadvantage of this approach,however, is that, as shown in FIG. 2 , at increased pH levels the amountof sodium ions taken up by the lithium ion sieve increases. In addition,if the pH is raised above 8, magnesium hydroxide may precipitate out ofsolution.

In one embodiment, the brine/lithium ion sieve slurry in the loadingreactor may be neutralized with an alkali, such as NaOH, in order tomaintain the pH so as to maximize the uptake of lithium while minimizingthe uptake of sodium. The pH may generally be greater than about 5 andless than about 9, preferably greater than 6 and less than 8. When thelithium ion sieve is MTA, the pH is preferably between 6 and 7.

Lithium is typically eluted from the LIS with an acid, such ashydrochloric acid, to concurrently regenerate the lithium ion sieve andproduce a lithium product, as shown by equation (2). The lithium ionsieve effectively neutralizes the acid by this reaction.LIS.Li+H⁺→LIS.H+Li⁺  (2)

As shown in FIG. 3 , the amount of lithium eluted from the lithium ionsieve increases as the concentration of HCl increases. For optimumelution efficiency, the acid concentration may be maintained at aconcentration of less than 0.1 M (defined as mol·dm⁻³ in FIG. 3 ). Asshown in FIG. 7 , for optimum elution efficiency, the acid concentrationmay correspond to a pH of less than 3 and greater than 1 and preferablyat a pH of approximately 2.

However, as also shown in FIG. 3 , at acid concentrations of greaterthan 0.1 M, increasing amounts of titanium are extracted from thelithium ion sieve, thereby degrading the lithium ion sieve and reducingits useful life. Above an acid concentration of about 0.1 M, excessiveamounts of titanium are extracted, resulting in a prohibitively shortlife.

One method to minimize such degradation of the lithium ion sieve is tominimize the contact time between the LIS and the acid. Because in oneembodiment the lithium ion sieve is in powdered form, the kinetics ofthe ion exchange process are quite rapid and the exchange reaction ofequation (2), above, is mostly completed in less than one hour. In anembodiment, the contact time between the LIS and the elution acid isless than one hour. Therefore, lithium is essentially completely removedfrom the lithium ion sieve while minimizing the degradation of thelithium ion sieve.

Additionally, the particle size of the lithium ion sieve particles playsa role in the design of the system described herein. FIG. 4 shows atypical particle size distribution of a sample of metatitanic acidlithium ion sieve taken after a few hours of air agitation in a slurry.The effective particle size (d₁₀) is about 0.5 μm and 90% (by volume) ofthe material is in the range of 0.4-40 μm. The effective size is thediameter of the particle for which 10 percent of the total grains aresmaller, and 90 percent of the total grains are larger, on a weight orvolume basis. The effective size of this material is about 0.5 μm. Whilethe coarser material may settle from a water slurry by gravity in lessthan one hour, the finer particles do not easily settle even after aday. Without intending to be bound by any particular theory, it isbelieved that larger lithium ion sieve particles are agglomerates offine particles produced by sintering during the synthesis process. As aresult, the large particles are susceptible to mechanical attritionduring mixing with the process liquids, so that there would be anincreasing proportion of fine particles over time. Consequently,separation of the lithium ion sieve from the process liquids by gravitysedimentation is not ideal.

Membranes are being increasingly used in bioreactors for wastewatertreatment. In a typical membrane bioreactor (MBR), microfiltration orultrafiltration membranes with pore sizes of less than 0.1 μm, either inhollow-fiber, tubular or flat sheet form, are submerged in a suspensionof wastewater and bio-solids. Clear filtered/treated wastewater is drawnthrough the membranes by vacuum. The wastewater/biosolids slurry istypically agitated by air sparging. Air agitation promotes oxygentransfer to the bio-solids and prevents membrane fouling due to build-upof bio-solids on the membrane surface.

In membrane bioreactors, the suspended solids concentration is typicallyless than 30 g/L and more typically 10-15 g/L. Higher suspendedconcentrations are not employed, as oxygen transfer is impeded due toresulting higher and non-Newtonian fluid viscosity. In addition, highersuspended solids concentrations reduce the membrane flux rate and/orincrease the trans-membrane pressure. Typical flux rates for submergedmembranes in membrane bioreactors are 10-30 liters per hour per squaremeter (which units are normally abbreviated as “LMH”).

In one embodiment, the submerged ultrafiltration or microfiltrationmembrane process may be used in the present invention as a means ofseparating the lithium ion sieve from the process liquids. The pore sizeof the membranes, at typically less than about 1 μm, is smaller than thesmallest lithium ion sieve particles, so nearly 100% solids separationcan be achieved. In the present invention, oxygen transfer is not anissue. However, submerged aeration (air agitation) may provide thenecessary mixing of the slurry, while the rising bubbles scour themembrane surfaces to reduce membrane fouling, and reduce the attritionand shearing of the LIS particles compared with mechanical mixing.

Embodiments described here are a significant departure from typicalimmersed membrane applications such as MBRs. Lithium ion sieve particlesallow treatment of much higher suspended solids concentrations whileachieving appreciable higher fluxes. Fluxes obtained in conventional MBRapplications are typically less than 30 LMH at transmembrane pressuresof 10-30 KPa and total suspended solids (TSS) levels of less than 30g/L. In contrast, with the present invention, fluxes as high as 300 LMHat transmembrane pressures of 20 KPa have been obtained with lithium ionsieves, at TSS levels of more than 100 g/L.

According to the present invention, the suspended solids concentrationmay be greater than about 50 g/L and preferably greater than 100 g/L.Without intended to be bound by any particular theory, it is believedthat a higher solids concentration in the reactor is advantageousbecause it reduces the reactor volume required to achieve a givenlithium ion sieve-liquid contact time.

In a fixed bed ion exchange system, the acid eluent becomes lower inacid concentration as it passes through the bed and is neutralized bythe reaction provided by equation (2) above. In order to maintain the pHof the acid in contact with the lithium ion sieve at less than 3, tomaintain elution efficiency, the pH of acid entering the bed may then beappreciably less than less than 1. Consequently, if the lithium ionsieve is regenerated in a fixed bed, the lithium ion sieve toward theentry end of the bed will be severely degraded by the more concentratedacid.

According to the present invention, the lithium ion sieve may beregenerated as a slurry in a reactor vessel where the lithium ion sieveis in contact with acid at a uniform concentration. The acidconcentration may be maintained at a concentration of less than 0.1 M,and preferably at an acid concentration corresponding to a pH of lessthan 3 and greater than 1 and preferably at a pH of approximately 2.This concentration can be maintained by continuously measuring the acidconcentration of the liquid in the reactor by suitable means and addingconcentrated acid as required, to maintain the concentration in thedesired range (e.g., at pH=2).

To minimize impurities, such as calcium, magnesium, potassium, andsodium, in the final lithium salt product produced by acid elution ofthe lithium ion sieve, the residual feed brine may be removed from thelithium ion sieve after loading and prior to acid elution by mixing theloaded lithium ion sieve with water and then separating out the water.In an alternative embodiment, the residual feed brine may be removed bydirectly filtering the loaded lithium ion sieve through a suitablefilter. According to the present invention, the preferred particle sizeof the lithium ion sieve is in the range of 0.4-40 μm. Solids particlesin this range can be filtered and de-watered using conventionalsolid/liquid separation devices, employing filter media, such as wovenfilter cloths with openings of greater than 10 μm in lieu of membraneswith pore sizes of less than 1 μm. Thus, the bulk of the feed brine willbe separated from the loaded lithium ion sieve. The dewatered lithiumion sieve may then be washed directly on the filter to remove theresidual brine from the lithium ion sieve without the necessity ofre-slurrying the lithium ion sieve in water. Exemplary types of filtersinclude, but are not limited to, horizontal belt vacuum and pressurefilters, rotary drum vacuum and rotary disk vacuum and pressure filters,pressure filter presses, and centrifuges.

As discussed above, elution of lithium from the lithium ion sieve withacid yields an acidic lithium salt solution. The lithium ion sieve ispreferably separated from the acidic lithium salt eluate solution tominimize the return of the recovered lithium with the regeneratedlithium ion sieve back to the loading reactor. A similar approach may beutilized as is used for separating feed brine from the loaded lithiumion sieve. Thus, the regenerated lithium ion sieve may be mixed withwater and then separating out the water. Alternatively, the lithium ionsieve may be filtered through a suitable filter, preferably one withwater washing capabilities.

Care should be exercised to minimize the moisture content of the lithiumion sieve transferred into the regeneration reactor. If excessiveamounts of water accompany the lithium ion sieve into the regenerationreactor, the recovered lithium salt eluate solution will be too dilute.Similarly, the lithium should be recovered with the liquid entrained onthe loaded lithium ion sieve that is withdrawn from the regenerationreactor.

As shown in Example 1 below, the working capacity of a metatitanic acidlithium ion sieve may be about 0.01 g lithium per gram of lithium ionsieve. The flow of lithium ion sieve on a dry basis would then be 100 glithium ion sieve/g Li recovered. When the slurry in the loading reactorcontains a suspended solids concentration of 100 g/L (i.e., about 90%moisture by weight and about 10% solids weight; 1 liter of water per 100grams lithium ion sieve) and this slurry was transferred directly to theregeneration reactor, it would bring (1 g lithium ion sieve/0.01 g Li/100 g/L lithium ion sieve)=1.0 liter of water per gram of lithiumrecovered. Ignoring the water in the concentrated acid, theconcentration of lithium in the eluate would then be 1 g/l.

If the suspended solids concentration in the regeneration reactor isalso maintained at 100 g/L and withdrawn at this concentration, theamount of lithium entrained with the regenerated lithium ion sieve wouldbe (1 liter/g Li×1 g/L Li)=1 g Li/g Li recovered. In other words, all ofthe lithium eluted from the lithium ion sieve would be withdrawn withthe lithium ion sieve. If this lithium ion sieve was then recycleddirectly back to the loading reactor, no net lithium would be recovered.

The regenerated lithium ion sieve slurry could be mixed with water in awashing reactor to recover the lithium values prior to recycling thelithium ion sieve to the loading reactor. To separate 90% of the lithiumfrom the lithium ion sieve would require 9 liters of water per gram ofrecovered lithium. The diluted liquid in the washing reactor could thenbe separated by gravity or a membrane, for example. The concentration oflithium would then be only 0.1 g/l. However, this concentration is toolow to be of practical use. Thus, the lithium ion sieve should bedewatered to a moisture content appreciably less than 90%.

For example, if the loaded lithium ion sieve slurry is dewatered to 50%moisture (i.e., 1 liter water/1000 g lithium ion sieve) the lithium ionsieve would carry only (1 liter water/1000 g lithium ion sieve)/(0.01 gLi/g lithium ion sieve)=0.1 liter water per gram of Li recovered.Ignoring the water in the concentrated acid, the concentration oflithium in the eluate would then be 10 g/liter.

Additionally, the regenerated lithium ion sieve should be dewatered whenit is removed from the regeneration reactor. Otherwise, a large portionof the recovered lithium will be recycled with the lithium ion sieveback to the loading reactor. Even if the regenerated lithium ion sieveis dewatered to a high degree, the lithium lost to the moistureentrained in the lithium ion sieve may be problematic. For example, ifthe regenerated lithium ion sieve is dewatered to 50% moisture contentby weight (i.e., 1 liter water per 1000 g of lithium ion sieve), theamount of lithium entrained with the lithium ion sieve would be (1liter/1000 g lithium ion sieve)/(0.01 g Li/g lithium ion sieve)×10 gLi/1 L)=1 g Li/g Li recovered. In other words, all of the lithium elutedfrom the lithium ion sieve would be withdrawn with the lithium ionsieve. If this lithium ion sieve was then recycled back to the loadingreactor, no net lithium would be recovered.

Thus, the lithium from the liquid entrained with the dewatered lithiumion sieve should be recovered. For instance, the regenerated lithium ionsieve may be washed with water. The lithium would then be recovered inthe wash water. The amount of wash water should be sufficient to recovermost of the lithium, but not so much as to excessively dilute therecovered lithium salt solution. One method to achieve this would be tore-slurry the lithium ion sieve in water and then re-filter the lithiumion sieve from the slurry. To wash 90% of the lithium from the lithiumion sieve would require about 9 mL of water per mL of entrained liquidin the lithium ion sieve, allowing recovery of a lithium salt solutioncontaining 1 g/L lithium under these conditions.

The amount of wash water can be reduced and the lithium concentrationcan concomitantly be increased by utilizing two or more counter-currentwashes. Accordingly, the dewatered lithium ion sieve recovered from thefirst wash stage is re-slurried in water once again in a second washstage and then dewatered yet again. The wash water recovered from thesecond stage dewatering device is utilized in the first wash stage inlieu of fresh water. With two counter-current wash stages, the amount ofwater required for 90% lithium recovery can be reduced from about 9 mLof water per mL of entrained liquid to about 3 mL of water per mL ofentrained liquid, and the concentration of recovered lithium can beincreased from 1 g/L to about 3 g/L.

In a further embodiment, the slurry may be dewatered by a device such asa horizontal vacuum belt filter. The dewatered lithium ion sieve cakemay then be washed directly on the filter. One or more count-currentwash stages can be employed on the filter. As another option, acentrifuge may be used. If a centrifuge is used, the solids may bere-slurried in water and then dewatered with the centrifuge. If severalwashing stages are used, the dewatered solids from a first centrifugemay be re-slurried with water again and then dewatered in a secondcentrifuge. The centrate from the second centrifuge may be used as thewater to slurry the solids feeding the first centrifuge. Additionalcentrifuges can be utilized in this manner to effectively achieve amulti-stage countercurrent solids wash.

If the particle size of the lithium ion sieve is too small, suchdewatering becomes more difficult. Indeed, even if the majority of theparticles are greater than 10 micrometers in diameter, the presence ofparticles much less than 10 micrometers in diameter makes dewateringdifficult. In particular, if the average particle size of the ion sieveis 0.1 μm or less, dewatering becomes virtually impossible.

In another embodiment of the present invention, the dry lithium ionsieve may be classified by a suitable device such as an air classifieror the wet lithium ion sieve may be classified by elutriation to removethe fine particles with a diameter of less than 1-10 micrometers. Bydoing so, separation of the lithium ion sieve from the liquid to betreated is facilitated. Removal of the fine particles will significantlyimprove filtration rates, avoid blinding of filtration media, andproduce a filter cake with a lower moisture content. By removing thefine particles in this manner, conventional solid/liquid separationdevices, such as horizontal belt vacuum and pressure filters, rotarydrum vacuum and rotary disk vacuum and pressure filters, pressure filterpresses, centrifuges, and the like may be more effectively employed.

To maximize the purity of the recovered lithium salt product, the feedbrine should be efficiently separated from the loaded lithium ion sieve.Purity requirements for battery grade lithium carbonate, for instance,are very stringent. Any residual feed brine retained with the loadedlithium ion sieve will contaminate the product with impurities in thefeed brine, such as calcium, magnesium, sodium, potassium, etc. As theconcentration of these impurities in the brine is much higher than thelithium, even minimal amounts of brine carry-over are problematic. Infact, the impurity contribution from entrained brine on the loadedlithium ion sieve is potentially greater than the quantity of impuritiesactually exchanged on to the lithium ion sieve in most cases. Whileadditional processes, such as lime/soda and ion exchange softening, canbe used to purify the recovered lithium solution, these additionalprocess steps involve additional capital and operating expense. However,efficient dewatering and washing of the loaded lithium ion sieve priorto passing it onto the regeneration reactor can minimize need for thesecostly processes. As discussed above, efficient dewatering can beachieved with conventional solids/liquid separation devices, providedthat the lithium ion sieve does not have significant quantities ofparticles less than 1-10 micrometers in diameter. In addition, the washwater requirements can be reduced by employing multi-stagecounter-current washing.

The present invention will hereinafter be described with reference toexemplary embodiments, which are written to be understood only asexamples and are not intended to limit the scope of the presentapplication.

EXAMPLE

A test unit was constructed to demonstrate the process according to oneembodiment of the invention. A schematic drawing of the test unit isshown in FIG. 5 .

The test unit consisted of six reactors (R1-R6), each one equipped withair agitation diffusers and five of which were equipped with immersedmembrane modules. Reactor R4, utilized for acid regeneration of thelithium ion sieve, was not equipped with a membrane. The working volumeof each of the reactors was approximately 5 liters with the exception ofthe reactor R4, which had a working volume of approximately 1.1 liter.

Lithium titanate (LTO) was used as the lithium ion sieve. The LTO wassynthesized by reacting lithium hydroxide with titanium dioxide at amolar ratio of approximately 2.2:1 at a temperature of 700° C. for 4hours. FIG. 4 , discussed above, provides the particle size distributionof the LTO used in this example. The initial LTO produced from thesynthesis was converted to metatitanic acid (HTO) by pickling the LTO in0.2 N HCl for 16 hours and then washing the resulting HTO with water.Reactor R1 and reactor R2 were initially charged with 100 g/L aqueousslurries of the LIS, while the remaining reactors were initially chargedwith 500 g/L slurries of the LIS. The lithium ion sieve was conveyedfrom reactor to reactor as a slurry by peristaltic pumps. The flow rateof the lithium ion sieve slurries was adjusted so that the solidstransfer rate was approximately 100 g/h on a dry weight basis.

The membrane modules were lab-scale immersed-type POREFLON™ units,manufactured by Sumitomo Electric Corporation, each having an effectivemembrane area of 0.1 m². Liquid was drawn through the membranes byvacuum using peristaltic pumps. The vacuum was maintained at less than40 kPa.

The lithium containing brine was made up from brine obtained from theSmackover formation in southern Arkansas and had a composition as shownin Table 1 below. After extraction of lithium from the brine inaccordance with the process, the brine was re-fortified with lithiumchloride and recycled to the process. As a result, the lithiumconcentration in the feed brine was somewhat higher than the initialbrine as received. The sodium and potassium concentrations wereestimated based upon published brine assays.

TABLE 1 TSS [Li] [Ca] [Na] [K] [Mg] Flow (g/L) (mg/L) (mg/L) (mg/L)(mg/L) (mg/L) (L/h) Feed 244 22,000 43,000* 1,384* 2,170 4.96 BrineBarren 61 4.15 Brine Product 4,300 1,400 9,770 76 0.54 Dilute 100 1.02slurry Conc. 500 0.21 slurry *Estimated from published brine assay data.

Reactor R1, the loading reactor, was equipped with a pH controller thatautomatically controlled the addition of 1 N NaOH such that a pH of 7.8was maintained. Thus, the acid generated by the ion exchange reactionwas continually neutralized. Feed brine was introduced to reactor R1 andallowed to contact the HTO. The HTO was fed to reactor R1 from reactorR6 as a 500 g/L slurry. As a result of the mixing of the concentratedslurry from reactor R6 with the feed brine, the solids concentration ofthe lithium ion sieve in reactor R1 was about 100 g/L. As the HTOextracted lithium ions from the brine, the HTO was partially convertedback to LTO. Lithium-depleted (i.e., barren) brine was drawn through themembranes by a pump.

The loaded lithium ion sieve (i.e., LTO) was withdrawn from the reactorR1 as a brine slurry and directed to reactor R2, which was the brinewash reactor. Water was fed to reactor R2 so that the residual brine waswashed from the LTO. The wash water was withdrawn from reactor R2through another immersed membrane module.

Loaded/washed LIS was withdrawn from reactor R2 as a water slurry anddirected to reactor R3, which was the thickener reactor. Water waswithdrawn from reactor R3 through another immersed membrane module, thusincreasing the solids concentration in reactor R3 to approximately 500g/L.

The thickened slurry of loaded/washed LIS at a solids concentration ofabout 500 g/L was withdrawn from reactor R3 and directed to reactor R4,which was the regeneration reactor. The lithium ion sieve in reactor R4was contacted with hydrochloric acid at a concentration of approximately0.2 M. The lithium ion sieve solids concentration in reactor R4 wasapproximately 500 g/L. The acid concentration was monitored andmaintained by a conductivity controller at a constant level through theaddition of 5 M HCl to a conductivity set point of 150 mS/cm. Contactingthe lithium ion sieve with acid converted it from the LTO form back tothe HTO form and resulted in a lithium ion sieve slurry of about 0.2 Mhydrochloric acid along with lithium chloride. Reactor R4 was notequipped with a membrane, and the lithium ion sieve slurry ofHCl/lithium chloride was simply allowed to overflow to reactor R5. It isrecognized that an acid concentration of 0.2 M is not preferred due toexcessive dissolution of titanium from the LIS, but this example stillillustrates the process of the present invention.

Reactor R5 was the first of two counter-currently operated acid washreactors. The majority of the HCl/lithium chloride was washed from thelithium ion sieve in reactor R5, while most of the residual HCl/lithiumchloride was washed from the lithium ion sieve in reactor R6. Thelithium ion sieve in reactor R5, at a solids concentration of about 500g/L, was contacted with wash-water from reactor R6. The acid wash-waterwas withdrawn from reactor R5 through another immersed membrane module.The acid wash-water withdrawn from reactor R5 constituted the recoveredlithium chloride product from the process. A slurry of lithium ion sieveat a concentration of about 500 g/L was withdrawn from reactor R5 anddirected to reactor R6.

Fresh water added to reactor R6 washed most of the remaining HCl/lithiumchloride from the lithium ion sieve. The wash-water was withdrawn fromreactor R6 through another immersed membrane module and directed toreactor R5. The concentration of lithium chloride in the wash-water inreactor R6 was thereby reduced to less than 10% of the lithiumconcentration in reactor R4. The lithium ion sieve/wash-water slurry waswithdrawn from reactor R6 and directed back to reactor R1 wherein it wasreused to extract lithium from the feed brine.

A continuous 12 hour test run was conducted. Aliquots of barren brineand product were sampled and assayed hourly. A graph showing the barrenand product concentrations over the course of the run is shown in FIG. 6. The results summarized in Table 1 were from 1-hour composite samplestaken after 10 hours of operation. The lithium concentration was reducedfrom 244 mg/L to 61 mg/L, a 75% recovery rate. The liquid residence timein the loading reactor was about 1 hour.

The lithium product contained a lithium concentration of 4,300 mg/L.More lithium was removed from the product (2,322 mg/h) than was actuallyextracted from the brine (957 mg/h). Without intending to be bound toany particular theory, it is believed that the difference (1,365 mg/h)was likely residual lithium on the lithium ion sieve that had not beencompletely removed from the LTO during the initial pickling in HCl.Based upon the lithium that was actually extracted from the brine, thelithium ion sieve capacity was 9.6 mg/g. The liquid residence time inthe strip reactor was 2.2 hours. Based upon the lithium that was loadedand recovered, the lithium concentration factor was about 10 times.

The feed brine contained a calcium concentration of 22,000 mg/L whilethe product contained a calcium concentration of only 1,400 mg/L. Theratio of calcium to lithium in the feed was 90. The ratio in the productwas 0.33. However, only about half of the lithium in the product wasactually extracted from the brine. If only the lithium in the productthat was extracted from the brine is considered, the ratio of Ca to Liin the product was 0.62, which represents an enrichment factor of90/0.62=145.

The feed brine contained an estimated sodium concentration of 43,000mg/L while the product contained a sodium concentration of only 9,770mg/L. The ratio of sodium to lithium in the feed was 176. The ratio inthe product was 2.3. If only the lithium in the product that wasextracted from the brine is considered, the ratio of Na to Li in theproduct was 4.3, which represents an enrichment factor of 176/4.3=41.

The feed brine contained a magnesium concentration of 2,170 mg/L whilethe product contained a magnesium concentration of only 76 mg/L. Theratio of magnesium to lithium in the feed was 8.9. The ratio in theproduct was 0.018. If only the lithium in the product that was extractedfrom the brine is considered, the ratio of Mg to Li in the product was0.034, which represents an enrichment factor of 8.9/.034=262.

Thus, the system and method described herein have the ability toselectively recover lithium from brines containing high concentrationsof calcium, sodium, and magnesium.

In this example, only one brine wash reactor was used, so some brinewould have passed into the regeneration reactor on the loaded lithiumion sieve, thus carrying some calcium, sodium, and/or magnesium into theregeneration reactor on the loaded lithium ion sieve. Without intendingto be bound to any particular theory, it is believed that the resultscould be improved by including a second brine washing reactor. Inaddition, as discussed above, by lowering the loading pH to 6-7, theamount of sodium loaded onto the lithium ion sieve could be reducedwithout appreciably decreasing the lithium capacity.

COMPARATIVE EXAMPLE

A key test was done in Chitrakar to evaluate the effect of HClconcentration on initial extraction of lithium and titanium from theadsorbent, which is shown in FIG. 4 a of Chitrakar. FIG. 4 a ofChitrakar shows the amount of lithium and titanium extracted as afunction of the HCl concentration. The data in Chitrakar shows that theHCl concentration should be 0.2 M or more. In fact, no data is shown inFIG. 4 a of Chitrakar for lithium extraction from the adsorbent below anacid concentration of 0.1 M, which is the preferred acid concentrationin which the present invention operates. In the present invention, thelithium and titanium components of the LTO adsorbent are extracted atmuch lower acid concentrations than predicted by Chitrakar.

References herein to terms such as “vertical,” “horizontal,” etc. aremade by way of example, and not by way of limitation, to establish aframe of reference. It is understood that various other frames ofreference may be employed for describing the invention without departingfrom the spirit and scope of the invention. It is also understood thatfeatures of the invention are not necessarily shown to scale in thedrawings. Furthermore, to the extent that the terms “composed of,”“includes,” “having,” “has,” “with,” or variants thereof are used ineither the detailed description or the claims, such terms are intendedto be inclusive and open-ended in a manner similar to the term“comprising.”

References herein to terms modified by language of approximation, suchas “about,” “approximately,” and “substantially,” are not to be limitedto the precise value specified. The language of approximation maycorrespond to the precision of an instrument used to measure the valueand, unless otherwise dependent on the precision of the instrument, mayindicate +/−10% of the stated value(s).

A feature “connected” or “coupled” to or with another feature may bedirectly connected or coupled to or with the other feature or, instead,one or more intervening features may be present. A feature may be“directly connected” or “directly coupled” to or with another feature ifintervening features are absent. A feature may be “indirectly connected”or “indirectly coupled” to or with another feature if at least oneintervening feature is present. A feature “on” or “contacting” anotherfeature may be directly on or in direct contact with the other featureor, instead, one or more intervening features may be present. A featuremay be “directly on” or in “direct contact” with another feature ifintervening features are absent. A feature may be “indirectly on” or in“indirect contact” with another feature if at least one interveningfeature is present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

While the invention has been illustrated by a description of variousembodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Thus, the invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. In theinterest of fully enabling persons ordinarily skilled in the art to makeand use the claimed invention, the applicant has provided information asto both advantages and disadvantages of various detailed embodiments.Persons of ordinary skill will understand that, in some applications,the disadvantages of a specific embodiment as detailed above may beavoided altogether or outweighed by the overall advantages provided bythe invention as claimed. Accordingly, departures may be made fromdetailed teachings above without departing from the spirit or scope ofapplicant's general inventive concept.

The invention claimed is:
 1. A process for recovery of lithium ions froma lithium-bearing brine, the process comprising: contacting thelithium-bearing brine with a lithium ion sieve for less than about onehour in a first reactor to form a lithium ion complex with the lithiumion sieve; separating the lithium ion complex with the lithium ion sievefrom the brine with a solid/liquid separation device; contacting thelithium ion complex with the lithium ion sieve with water beforedecomplexing in a second reactor; and decomplexing lithium ions from thelithium ion sieve in the second reactor to form an acidic lithium salteluate solution separated from the lithium ion sieve; separating thelithium ion sieve from the acidic lithium salt eluate solution with asolid/liquid separation device; and contacting the lithium ion sievewith water after decomplexing in the second reactor to obtain aregenerated lithium ion sieve and a dilute acid water wash; wherein thelithium ion sieve comprises an oxide of titanium or niobium; wherein apH of the first reactor is maintained at a constant value throughaddition of an alkali; wherein the decomplexing is performed by elutionusing an acid; wherein an average contact time of the lithium ioncomplex with the lithium ion sieve and the acid is less than 1 hour;wherein a concentration of the acid is maintained at a constant valuethrough additions of said acid; and wherein the concentration of theacid is less than 0.1 M.
 2. The process of claim 1, wherein the pH ofthe acid is greater than 1 and less than
 3. 3. The process of claim 1,wherein the pH of the acid is approximately
 2. 4. The process of claim1, wherein the pH is maintained at the constant value of greater than 4and less than
 9. 5. The process of claim 1, wherein the pH in the firstreactor is greater than 6 and less than
 8. 6. The process of claim 1,wherein more than 90% of the lithium ion sieves have an average particlediameter of less than 40 μm and more than 90% of the lithium ion sieveshave an average particle diameter of greater than 0.4 μm.
 7. The processof claim 6, further comprising removing lithium ion sieves having anaverage particle diameter of less than 1 μm before contacting thelithium-bearing brine with the lithium ion sieve.
 8. The process ofclaim 1, wherein more than 90% by volume of particles of the lithium ionsieve are less than 100 μm in diameter and greater than 0.5 μm indiameter.
 9. The process of claim 1, wherein more than 90% by volume ofparticles of the lithium ion sieve are greater than 0.5 μm in diameter.10. The process of claim 1, wherein the lithium ion sieve comprisesmetatitanic acid.
 11. The process of claim 1, further comprising: addingthe regenerated lithium ion sieve to the first reactor.
 12. The processof claim 11, further comprising adding the dilute acid water wash andadditional concentrated acid to the second reactor.
 13. The process ofclaim 11, further comprising dewatering the lithium ion complex with thelithium ion sieve to a moisture content of less than 90% by weightbefore decomplexing the lithium ion from the lithium ion sieve in thesecond reactor.
 14. The process of claim 11, further comprisingdewatering the regenerated lithium ion sieve before being added to thefirst reactor.
 15. The process of claim 11, wherein contacting thelithium ion sieve with water comprises contacting the lithium ion sievewith sufficient water such that more than 50% of the lithium ion thathas been decomplexed from the lithium ion sieve is washed from thelithium ion sieve prior to adding the regenerated lithium ion sieve tothe first reactor.
 16. The process of claim 15, wherein contacting thelithium ion sieve with water comprises contacting the lithium ion sievewith water in more than one counter-current stage such that more than50% of the lithium ion that has been decomplexed from the lithium ionsieve is washed from the lithium ion sieve prior to adding theregenerated lithium ion sieve to the first stirred reactor.
 17. Theprocess of claim 1, wherein the first reactor comprises ultrafiltrationor microfiltration membranes.
 18. The process of claim 17, wherein airis used to agitate contents of the first reactor.
 19. The process ofclaim 17, wherein a flux rate through the ultrafiltration membrane orthe microfiltration membrane is greater than 30 LMH at transmembranepressures of less than 30 kPa.
 20. The process of claim 1, wherein aconcentration of the lithium ion sieve is greater than 50 g/L.
 21. Theprocess of claim 1, wherein the alkali comprises sodium hydroxide,ammonium hydroxide, anhydrous ammonia, potassium hydroxide, sodiumcarbonate, magnesium hydroxide, or calcium hydroxide.
 22. The process ofclaim 1, wherein the acid comprises hydrochloric acid or sulfuric acid.23. The process of claim 1, wherein a concentration of the lithium ionsieve is greater than 100 g/L.
 24. The process of claim 1, wherein thealkali comprises anhydrous ammonia or ammonium hydroxide.